The present invention relates to a method of manufacturing a ferroelectric thin film and a method of manufacturing a ferroelectric memory, particularly to improve the crystallinity of the ferroelectric thin film.
The ferroelectric memory being researched now is divided into two main areas. One is directed to a system for detecting reverse charge quantity of a ferroelectric capacitor constructed with the ferroelectric capacitor and a selective transistor.
Another is directed to a memory of a system for detecting a change of resistance of a semiconductor caused by a spontaneous polarization of the ferroelectric substance. A typical example of this type of system is a MFSFET. This is an MIS structure using the ferroelectric substance for a gate insulating film.
In any structure, it is known that film quality of the ferroelectric substance affects the characteristics of memory significantly.
Then, various methods for improving the crystallinity of the ferroelectric thin film are proposed. As one of them, a method of crystallization of a PZT thin film called Ti seed method is proposed.
As shown in FIG. 7, the method includes forming a seed layer 9L consisting of titanium ultra thin film of about 20 nm film thickness on a surface of a lower electrode 8 consisting of platinum Pt and the like by spattering method and to form a PZT film 9P on the upper layer by sol-gel method as shown in FIG. 7. Here, mixed solution of Pb(CH3COO)2.3H2O, Zr(t-OC4H9)4, and Ti(i-OC3H7)4 is used as a starting material, after spin-coating the mixed solution, is dried at 150xc2x0 C., and temporary baking of 400xc2x0 C. for 30 minutes is performed under a dry air atmosphere. After repeating this five times, crystal growth from the ultra thin film 9L appears through crystallization annealing process of about 700xc2x0 C., one minute in atmosphere of O2.
In the method, there has been a problem that particle diameter of crystal can not be controlled because a place where crystallization starts is unstable and dispersion of characteristic is large because uniform size columnar crystal is formed so as not to obtain suitable characteristics, particularly at micronization and high integration.
There has been a problem that the method has a place becoming titanium oxide layer (TiO2) or lead titanate (PbTiO3) layer without becoming PZT film so as to obtain good characteristics.
There has been a problem that the method negatively affects the substrate layer, for example, by negatively affecting substrate wiring because the temperature at crystallization annealing is high at about 700xc2x0 C.
The invention is performed in view of the circumstances, and an object of the invention is to provide a ferroelectric thin film that is uniform and good in crystallinity.
The invention is characterized by forming a seed layer including ultra-fine particle powder including composing element of a ferroelectric substance thin film on a surface of a substrate constructing the substrate before forming the ferroelectric substance thin film and forming the ferroelectric substance thin film on an upper layer of the seed layer so as to performing crystallization making the seed layer a nucleus.
According to such a construction, it is possible to obtain a ferroelectric thin film that is uniform and good in crystallinity because crystallization advances well making the ultra-fine particle powder a nucleus by existence of the ultra-fine particle powder. It is desirable to make the ultra-fine particle powder from 0.5 nm to about 200 nm particle diameter, particularly from 1 nm to about 50 nm particle diameter.
Incidentally, some minimum number of atoms is needed for the ultra-fine particle powder to become a nucleus, as the ultra-fine particle powder can not become the nucleus with one atom, and it is desirable to be sufficiently larger than the atomic size of about 0.1 nm. On the other hand, when the nucleus is too large, the center of the nucleus remains as Ti. Therefore, high annealing temperature is needed for converting Ti. It is impossible to form a flat and uniform ferroelectric thin film when the size is larger than 200 nm. The nucleus is hard to scatter in solution when the nucleus is large.
Further, the concentration is desirable to be from 0.00001 wt % (0.1 wtppm) to about 1 wt %.
Desirably, the invention is characterized by including a process forming a seed layer including titanium ultra-fine particle powder becoming a seed and a process forming a PZT thin film on the upper layer of the seed layer.
According such a construction, it is possible to obtain a PZT ferroelectric thin film that is uniform and good in crystallinity because crystallization advances well, thereby making the titanium ultra-fine particle powder a nucleus by the presence of the titanium ultra-fine particle powder of about 5 nm diameter.
Desirably, the invention is characterized by that the process forming the seed layer includes a process for applying a solution that includes the titanium ultra-fine particle powder and a process for drying and baking.
According to such a construction, it is possible to arrange the titanium ultra-fine particle powder easily and uniformly.
Desirably, the invention is characterized by that the process forming the PZT thin film includes a spattering process.
Desirably, the process of forming the PZT thin film further includes an annealing process for crystallization.
According to such a construction, it is possible to easily form a good ferroelectric thin film in crystallinity by introducing an annealing process for crystallization. However, it is also possible to perform crystallization at a heating process in the following forming process or to form an electrode with an insulating film too, because crystal growth takes place at about 450xc2x0 C., which is a lower temperature than that used by the related art.
The second method of the invention is characterized by including a process for applying a ferroelectric thin film liquid that includes ultra-fine particle powder comprising at least one kind of composing elements of the ferroelectric thin film on a surface of a substrate. A baking process is also included.
According to such a construction, crystallization from the ultra-fine particle powder advances well by forming a thin film that includes ultra-fine particle powder. Thus, it is possible to form a thin film that is uniform and high in reliability.
Desirably, the invention is characterized by including a process for applying a PZT applying liquid that includes ultra-fine particle powder that becomes a seed on a surface of a substrate. A baking process is also included.
According to such a construction, crystal growth starts from a seed consisting of titanium ultra-fine particle powder of about 5 nm particle diameter scattered uniformly throughout the ferroelectric thin film. Therefore, it is possible to form a PZT ferroelectric thin film that is uniform and good in crystallinity because crystallization advances well, thereby making the titanium particle powder a nucleus.
Desirably, the invention is characterized by further including an annealing process for crystallization.
According to such a construction, it is possible to form easily a good ferroelectric thin film in crystallinity by introducing an annealing process for crystallization. However, it is possible to perform crystallization at a heating process in the following forming process or to form an electrode with an insulating film too, because crystal growth takes place at about 450xc2x0 C., which is a lower temperature than that used by the related art.
The third invention is characterized in that forming the ferroelectric film is performed by forming a seed layer including an ultra-fine particle powder. The ultra-fine particle powder includes a composing element of the ferroelectric thin film on a surface of a floating gate before forming the ferroelectric substance thin film. Crystal growth makes the ultra-fine particle powder a nucleus for a method of manufacturing a ferroelectric consisting of an FET of an MFMIS structure.
According to such a construction, it is possible to obtain a ferroelectric thin film that is uniform and good in crystallinity because crystallization advances well, thereby making the ultra-fine particle powder a nucleus through the presence of the ultra-fine particle powder of about 5 nm diameter. Thus, it is possible to form a ferroelectric memory that is high in reliability.
In the fourth invention, a forming process of the ferroelectric film is performed by applying a ferroelectric thin film applying liquid. The liquid includes an ultra-fine particle powder comprising at least one kind of composing elements of the ferroelectric thin film on a surface of a substrate. The ferroelectric thin film is formed so as to make it crystallize to produce a ferroelectric memory consisting of an FET of an MFMIS structure.
According to such a construction, a uniform ferroelectric thin film is obtained because crystal growth starts from a seed scattered uniformly throughout the ferroelectric thin film, and it is possible to form a ferroelectric memory that is high in reliability at micronization.
The fifth invention is characterized in that a ferroelectric thin film of the ferroelectric capacitor is formed by applying a ferroelectric thin film applying liquid. The liquid includes ultra-fine particle powder comprising at least one kind of composing elements of the ferroelectric thin film on a surface of a first electrode. Crystallization is performed to produce a ferroelectric memory consisting of a switching transistor and a ferroelectric capacitor.
According to such a construction, a uniform ferroelectric thin film is obtained because crystal growth starts from a seed scattered uniformly throughout the ferroelectric thin film, and it is possible to form a ferroelectric memory that is high in reliability at micronization.
The sixth invention is characterized in that a ferroelectric thin film of the ferroelectric capacitor is formed by forming a strong seed layer including ultra-fine particle powder. The powder includes at least one kind of composing elements of the ferroelectric thin film on a surface of a first electrode. The ferroelectric thin film is formed on an upper layer of the seed layer. The ferroelectric thin film comprises crystals of all sizes. Crystallization produces a ferroelectric memory consisting of a switching transistor and a ferroelectric capacitor.
According to such a construction, it is possible to obtain a ferroelectric thin film that is uniform and good in crystallinity because crystallization advances well, thereby making the ultra-fine particle powder a nucleus and to form a ferroelectric memory high in reliability by existence of the titanium ultra-fine particle powder of about 5 nm diameter.